Update community instance URL in README

https://fmd.nulide.de/ has moved to https://server.fmd-foss.org/. See https://fmd-foss.org/blog/2025/11/08/new-server

The old URL will continue to work for the foreseeable future

Author: devinslick

README.md

@@ -208,7 +208,7 @@ This client targets the FMD ecosystem:
 
 - https://fmd-foss.org/
 - https://gitlab.com/fmd-foss
-- Public community instance: https://fmd.nulide.de/
+- Public community instance: https://server.fmd-foss.org/
  - Listed on the official FMD community page: https://fmd-foss.org/docs/fmd-server/community
 
 MIT © 2025 Devin Slick